DE 19 511 534 A1 teaches a prior art method and arrangement in which the 3D characteristics of a moving surface are inspected by illuminating the surface from at least two different illumination directions with light sources, the light sources of each illumination direction illuminating the surface with a light of a different color than the other illumination directions. The object's surface is illuminated simultaneously from the different illumination directions, and the so illuminated surface is imaged with a camera to provide image information for analysis. The analysis of the 3D characteristics of the object's surface is based on color classification, with which the color values detected on the surface are compared.
The prior art method and arrangement allow the inspection of the 3D characteristics of the object's surface but not of the glossiness and reflectivity of the surface, since symmetrical dark field illumination from two illumination directions is used in the method. The fact that the 3D analysis is based on color classification impairs the method: for example, the method is not able to adjust to a change in the surface material of the object's surface, in which the surface material changes either completely or changes to a different variety of the same surface material or both, and neither is it able to adjust to changes in the illumination. This causes false alarms, which poses a major problem particularly in production processes.
On account of the above, the prior art method thus has a very limited ability to differentiate between different anomalies on the object's surface.